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Summary of Section 13.1: Overview of Mass-Storage Structure

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Mass-storage in modern computing primarily relies on hard disk drives (HDDs) and nonvolatile memory (NVM) devices. This section details their mechanisms, performance characteristics, and how operating systems handle address mapping.

Hard Disk Drives (HDDs)

HDDs store data magnetically on spinning platters. Key components include:

• Platter: Circular disks coated with a magnetic layer.
• Read-Write Head: Moves over platters to read/write data.
• Disk Arm: Holds the read-write heads and moves them across the platters.
• Tracks & Sectors: Platters are divided into circular tracks, which are subdivided into sectors (smallest storage unit).
• Cylinder: A set of tracks across multiple platters aligned at the same disk arm position.

Performance Metrics

• Transfer Rate: Speed of data flow between the drive and the system.
• Seek Time: Time to move the disk arm to the desired track.
• Rotational Latency: Time for the desired sector to rotate under the read-write head.
• Head Crash: A failure where the read-write head contacts the platter, damaging data.

HDDs are still widely used, but their mechanical nature makes them slower and more prone to failure compared to NVM devices.

Nonvolatile Memory (NVM) Devices

NVM devices, such as solid-state drives (SSDs) and flash memory, store data electronically rather than magnetically. They offer advantages over HDDs: